Vehicle headlight



Nov. l24,v 1942- J. J. SHERIDAN Erm. 2,302,979

vlsmlma HEAD LIGHT Filed Jan.. 21. 1941v z'sheets-sheet 1 Nav. 24, 1942,J, J; SHERIDAN E; Ag f 2,302,979

VEHICLE HEAD LIGHT Filed Jan. 21. 1941 2 sheets-sheet 2' INVENTQRS J.J.Sher' dan W.A.H ornng D.L.Dearborn Patented Nov. 24, 1942 UNITED STATESPATENT OFFICE VEHICLE HEADLIGHT Joseph J. Sheridan, San

Mateo, Robert L.

Application January 21, 1941, Serial No. 375,298

2 Claims.

This invention relates to improvements in Vehicle headlights and moreparticularly to a reflector designed to give a downwardly directedillumination.

Our invention comprises a reector having a contour which is so shapedand positioned with respect to a light source of known iinite size andshape, that the luminous flux is distributed in a vertical. plane inaccordance with a predetermined illuminated pattern wherein there aresubstantially no light rays directed thereabove. A reflector made inaccordance with our invention is particularly adapted to direct lightrays so there is substantially no glare in the eyes of motorists who inthe normal course of driving are proceeding vin the opposite direction.

In order that objects above the level of the surface of the highway bevisible, it is necessary that a small part of the light flux be directedabove a horizontal plane intersecting the Vertex of the reflector. Byhaving this upwardly directed part of the light flux also directedsubstantially to the right there is no glare in the eyes of personsproceeding normally in the opposite direction, and still therequirements as to the illumination of objects above the horizontal aresatised. Upwardly directed rays must be accurately controlled to avoidglare and there must be no uncontrolled, aberrant rays which, in causingglare, constitute a negative factor in visibility, thereby reducing theeffectiveness of the illumination aiorded by the headlights.

These results are attained by designing a reilector, not paraboloidal,but one embodying that perturbation from a paraboloid capable ofreflecting the light rays from a light source of nite size and shape soas tc produce the lumen distribution in the emitted light beam fulllingpredetermined calculations and legal requirements for visibility.

Our invention will be better understood from the following descriptiontaken in connection with the accompanying drawings, in which:

Fig. 1 is a table showing the horizontal and vertical candlepowerdistribution of light ilux on an illuminated pattern as a typicalrequirement; Fig` 2 is a graph showing relative light flux distributionwith respect to a dihedral angle. Curve I represents the idealrequirement for flux distribution with respect to dihedral angle a;curve II represents the flux distribution of a true paraboloid whereinthe light source is located about one and one-half inches from thevertex of the paraboloid and all of the source is located above thefocal point of the paraboloid (Cl. 24U-41.35)

and in the Y-Z plane; and curve III represents the light ux distributionfrom a reector embodying our invention, the contour of which differsfrom a true paraboloid by a calculated amount constituting theperturbation therefrom, and which perturbated paraboloid has its lightsource located approximately three inches from the Vertex V, all of saidlight source being positioned in a plane passing through the axis Y-Yand Z-Z and above the focal point So;

Fig. 3 is a diagrammatic illustration showing a reflector embodying theprinciples of our invention in Vertical section, the curvature of saidreflector being shown in full lines and that of a true paraboloid beingshown by a single line, there being also shown certain geometricalprinciples on which our device is based;

Fig. 4 is a front view of the reflector embodying the principles of ourinvention, there being also shown certain geometrical principles onwhich our device is based; and

Fig. 5 is a vertical section taken through a reflector embodying ourinvention, showing by the dotted lines a true paraboloid.

There are ve factors which are considered as being basic in thedevelopment of a formula for a reflector contour embodying theprinciples of our invention, namely: (a) That the light source orfilament of the headlamp be not a point, but one of definite and knownsize and shape; (bi) when considering the requirement as to iluxdistribution on an illuminated pattern that the light source of deniteand known size and shape be positioned at a predetermined distance fromthe vertex of the reilector; (c) with the size, shape and position ofthe light source being known, as well as the requirement as to iluxdistribution on an illuminated pattern, that the amount of perturbationof the reilector from a true paraboloid be such as to satisfy the saidrequirements as to ilux distribution; (d) that the light source beshielded so no rays can emanate outwardly from it in a direction abovethe horizontal; and (e) that the vertical angle subtended by the lightsource at the vertex or at the point on the reflector contour nearest tothe said source, shall not exceed two degrees when the vertical anglesubtended by the principal part of the illuminated field is fourdegrees; or, in other words, that this ratio shall be:

angle 1:1@ angle a Since the design of the contour of the reflectorsurface is dependent primarily upon the vertical distribution of theluminous flux at the illuminated pattern, it is essential that saiddistribution be determined at the outset. A distribution, typical ofsuch a requirement is shown in Fig. 1, which shows horizontal angle aswell as vertical angle candlepower distribution. Curve I shown on Fig. 2is derived from the said table of Fig. l by computing lumen distributionin each vertical angle zone from the candlepower distribution in eachcorresponding vertical angle zone. Curve I, therefore, provides onebasis upon which the reflector contour will be designed.

The requirement as to distribution of light flux on the illuminatedpattern is illustrated graphically by Fig. 2 in which the ordinate is inrelative luminous flux per degree of dihedral angle and the abscissa isin degrees of dihedral angle. This dihedral angle is defined as theangle between the horizontal plane through the focal point of thereflector and any plane through the Z axis.

A true paraboloid in which the source is one and one-half inches or lessfrom the vertex,vor subtends an angle at the vertex of four degrees ormore will give rise to the flux distribution shown by curve II,approximately, providing all of the source be above the focal point.

This large deviation from the requirement indicated by curve I, wepr'opose to eliminate by increasing the distance from the source to thereilector vertex and by changing the shape of the reflector contour by acertain calculated amount, thus producing the flux distribution curveIII, and very closely approximating the required curve I.

To satisfy this requirement and produce curve III, the calculation ofthe amount by which our reflector contour differs from the contour of atrue paraboloid will be explained in terms of the symbols of Fig. 3. Inthis figure, X-X is the axis of the reflector and is a horizontal linethrough the focus and the vertex of the true paraboloid with which thecalculation starts; Y-Y is a vertical line through this focus; P is thecontour of the true paraboloid; V is the vertex of the true paraboloid;R is the contour of the perturbed paraboloid producing the fluxdistribution of curve III, Fig. 2; p is the difference in the radiusvector of the true paraboloid and that of the perturbed paraboloid; isthe angle between the X axis and a typical ray from a point on thesource; N is the point of incidence of this ray on the reflectorcontour; NN is the reflected ray; NA is a line parallel to the X axis; ais the angle between the X axis and the projection on the XY plane ofNN; d is the angle subtended at V by the source S; S0 and Sn are theextreme points of the source in a vertical plane.

The quantity, p, the perturbation which must be added to the trueparaboloid in order to produce the required reflector contour isobtained by expressing it as a power series in 0 or of angle a withunknown coefcients; by substituting in the formula for flux distributiondue to a single point of the source; integrating over the source;equating the result to the required function of angle a shown by curveI, Fig. 2. This last step fixes the values of the unknown coefficientsand makes p a known function of 6.

For the numerical requirements shown by curve I, and for the distanceV-SO equal to three inches, or angle d equal to 2, and for all of thesource located above S0, in Figs. 3 and 4, the perturbation, p, equals0.011 02 inch, with angle 0 expressed in radians.

r is the radius vector of paraboloid P. The

radius vector of the reiiector Ris r-HJ. The light shield is designatedby the numeral 6.

To the open face of the reflector must be added a v cover glass havingcertain optical properties.

'By means of vertical flutes, or cylindrical lenses,

properly designed for use with the reflector above described, thevertical or dihedral angle flux distribution can be redistributedhorizontally on the illuminated pattern in any desired relative densitynecessary to satisfy the existing laws, regulations or otherrequirements determined from practical needs for the device.

As an example, we have described our invention as being particularlyuseful as a vehicle headlight. It is apparent, however, that theprinciples of our invention are equally applicable to searchlights,oodlights or lamps of various kinds, so for this and other obviousreasons it is to be understood that our invention is to be broadlyincluded within the scope of the appended claims.

Having described our invention, what we claim l. In a light projector,the combination comprising a light source of predetermined size andshape, a reflector positioned to reflect light rays emanating from saidsource, said reflector being so positioned with respect to said sourcethat the angle subtended by said source at the Vertex of the reflectoris substantially two degrees, the said source being located at and abovethe focal point of the reflector, the said reector having an effectivesurface which is generated by the revolution of a curve that varies froma true paraboloid by a certain perturbation, the said perturbation beingdetermined by the use of the coordinate formula p=(0.011iC) 62 in whichp is given in decimals of an inch and 0 is given in radians between thelimits of zero and pi over two and C has a value greater than zero andless than 0.011, and means for preventing the emanation of light raysupwardly and forwardly.

2. In a light projector, the combination comprising a light source ofpredetermined size and shape, a reflector positioned to reflect lightrays emanating from said source, said reflector being so positioned withrespect to said source that the angle subtended by said source at thevertex of the reflector is substantially two degrees, the said sourcebeing located at and above the focal point of the reflector, the saidreflector having an effective surface which is generated by therevolution of a curve that varies from a true paraboloid by theperturbation p thereof, and which curve is determined by use of thepolar coordinate formula 6 mtr-.awww

in which r is the radius vector in inches, 0 is the polar angle inradians and varies between radians, 7c is one when the latus vectumequals twelve inches and varies directly with the latus vectum, p equals0.011 02, inches.

f zero and pi over two JOSEPH J. SHERIDAN. ROBERT L. DEARBORN. WENDELLA. HORNING.

